Senator Elizabeth Warren and the app developer community are speaking out against Apple after the company rejected an update to Spotify’s iOS iPhone app earlier this week.

Apple cited "business model rules" as the reason for turning down a Spotify update to its iOS app. Spotify claimed the rejection was an anti-competitive measure and suggested that Apple was using its approval process to hurt competitors of Apple Music, according to a letter from Spotify’s legal team to Apple.

Spotify sent copies of its letter to select Congressional staff in Washington, D.C. In response, Warren said that “Apple has long used its control of iOS to squash competition in music.”

Jake Ward, president and CEO of the Application Developers Alliance, also admonished Apple for denying choices to consumers.

“For the app marketplace to continue to thrive, users to have choices, and developers to have a competitive opportunity, platforms must give publishers clear and consistent guidelines," Ward wrote in a statement on Thursday. "Platforms deliberately creating friction and obstacles between publishers and users is bad for business and ultimately hurts consumers.”

Spotify general counsel Horacio Gutierrez sent a letter to Apple on June 26 that said the rejection is "causing grave harm" to users. The letter claimed that Apple won't approve the new app version because Spotify doesn't use the company's billing method for in-app purchases and subscription services.

"This latest episode raises serious concerns under both U.S. and EU competition law," Gutierrez wrote. "It continues a troubling pattern of behavior by Apple to exclude and diminish the competitiveness of Spotify on iOS and as a rival to Apple Music, particularly when seen against the backdrop of Apple’s previous anticompetitive conduct aimed at Spotify."

Spotify recently launched a promotion that gave new users three months of service for $1 if they signed up online. When Spotify attempted to promote the campaign inside the app, Apple threatened to remove the app from its store. Spotify dropped the in-app promotion, but turned off the iTunes billing option in iOS, which led to the current animosity.

Apple Music launched more than a year ago and attracted 15 million of subscribers, about half as many as Spotify. Apple Music launched at the same price point as Spotify, but many users complained Apple Music didn’t build social networking and playlist sharing features up to par with Spotify.